I'd look for air intrusion from between the filter head and the hardline. The slightest air leak there could allow the fuel to drain back to the tank when parked nose up.
On level ground, the tank is actually higher than the plumbing, keeping fuel up near the lift pump by way of gravity.
Since you were able to restart the car rather quickly, that tells me the lift pump itself is fine, properly drawing fuel up the lines.
I'd inspect all rubber... from the hardline to the lift pump, and from the lift pump to the filter head.
Also check the hand primer. If you've got the plastic headed twist lock type, they've been known to leak, especially after 30 years.
HtH..